1. Field of the Invention
The present invention is concerned with the field of removing fluid contaminants from solid materials, and in particular, with a method and apparatus for removing such contaminants from the ground in an economical and ecologically safe manner.
2. Description of the Art
Soil contamination resulting from petrochemical spills, toxic waste spills, radioactive wastes, and other chemicals presents a potentially serious problem. Such contaminants may find their way beneath the surface of the earth to the level of the water table below, thereby contaminating such water with potentially catastrophic and expensive consequences. A particular hazard is presented by underground storage tanks used for the storage of gasoline, solvents and other petrochemicals. Because the storage tanks are so often underground, leaks that may develop as a result of corrosion or earth movement may remain undetected for significant periods of time, during which the hazardous materials stored in such tanks continue to seep into the ground presenting a threat to the water table. In some cases, such tanks become abandoned and forgotten, often while some of the hazardous materials remain inside.
Presently, when it is discovered that an underground tank being used for the storage of petrochemicals or other toxic material is contaminating or presenting a serious danger of contaminating the soil, the tank and the contaminated soil are both removed. First, the ground surface above the tank, which may be asphalt or concrete, is removed. The tank is then drained of any residual fluid and partially backfilled with an absorbent agent before the tank is removed from the ground. The ground around the tank is then profiled to determine where the soil has been contaminated from the leakage from the tank. The contaminated soil is then removed from the ground, loaded in trucks, and hauled from the site. Other soil must be brought in to replace that which is removed. However, as the removed soil is still contaminated, there still remains a problem of what to do with the contaminated soil. Presently, in some instances, such soil is trucked several hundreds miles or more. The soil is spread in a relatively thin layer over the surface of the desert, for example, where the level of the water table is located at some depth below the surface of the earth and where the contaminated soil may be aerated so that the contaminated materials are eventually evaporated, assisted by the heat in the desert environment. It will be appreciated that the removal of soil in such a manner, at least for the short term, merely results in the contaminated soil being relocated at considerable expense and the problem not being eliminated.
It will be appreciated that not only is the present method of eliminating contaminants from the ground by in fact removing the contaminated ground expensive because of the necessity of having to haul the contaminated soil to another area, but in some cases, such soil may not be able to be removed without presenting a danger to nearby structures which may require that earth for their support.
Similar problems attend the remedying of soil contamination resulting from spills of petrochemicals or other toxic materials and radioactive material. Such materials may form plumes having a migratory nature, i.e., moving vapor clouds within the earth, that may eventually find their way to the water table or to other locations where they may present a threat to health and safety.
It is therefore a primary object of the present invention to provide a method and apparatus for removing contaminants from the soil in an efficient and ecologically sound manner in which most of the contaminated soil need not be removed from the ground. Another object of the present invention is to enable the removal of contaminants from the ground in a manner which allows their collection and subsequent disposition, if desired. An additional object of the present invention is to provide a method and apparatus by which the level of the ground contamination may be monitored, so that the process of removing the contamination may be terminated when a level of contamination below that which is considered unsafe is all that remains. Still, an additional object of the present invention is to achieve the above objects in a manner which may provide benefits to the soil through induced aeration and the introduction of nitrogen gas.
More generally, the present invention has for an object the providing of a method and apparatus for the removal of fluid contamination from an essentially solid material, the removal of contaminants from the soil being an important example.